1. Field of the Invention
Exemplary embodiments of the present invention relate to wireless power transmission technology; and, more particularly, to an apparatus for feeding power to a resonator, without separate impedance matching, and a transmitter and receiver using the same.
2. Description of Related Art
A conventional RF energy transmission technology using a self resonator having a nonradiative characteristic may be categorized into “symmetric resonance type wireless power transmission technology” and “asymmetric resonance type wireless power transmission technology.” The symmetric resonance type wireless power transmission technology uses a resonator to make both of a transmitting resonator and a receiving resonator at the same frequency. The asymmetric resonance type wireless power transmission technology uses a resonator at one side and a non-resonator at another side. As an example of a symmetric resonance type wireless power transmission scheme, both of a transmitting resonator and a receiving resonator using an indirect feeding method are configured with three-dimensional helical type loop resonators, as illustrated in FIG. 1. As an example of an asymmetric resonance type wireless power transmission scheme, a receiving resonator using an indirect feeding method is used as a receiving device, and a three-dimensional helical type loop resonator using a direct feeding method is used as a transmitting device, as illustrated in FIG. 2.
Referring to FIG. 1, in the case of the symmetric resonance type wireless power transmission scheme, impedance matching in a transmitting resonator and a receiving resonator is achieved by adjusting a gap G between a feeding loop line and a helical type resonator. Thus, it is inconvenient in real application and an additional mounting space is required as much as the gap G between the feeding loop line and the helical type resonator.
Referring to FIG. 2, in the case of the asymmetric resonance type wireless power transmission scheme, a receiving unit has the same configuration as that in the symmetric resonance type wireless power transmission scheme. That is, the receiving unit requires a reception impedance matching circuit for adjusting a gap between a feeding loop line and a receiving resonator. Thus, it is inconvenient in real application and an additional mounting space is required as much as the gap between the feeding loop line and the receiving resonator. In terms of input impedance as illustrated in FIG. 3, a resistance and a reactance of a transmitting loop resonator are maintained at approximately 20Ω and approximately −50Ω, respectively, even though a transmitting unit performs a direct feeding. Thus, it is difficult to use a 50-Ω cable which has been widely used, and a separate transmission impedance matching circuit is required. The use of the impedance matching circuit lowers power transmission efficiency as much. In other words, since the asymmetric resonance type wireless power transmission scheme requires a separate matching circuit for maintaining the impedance matching, the power transmission efficiency thereof is lowered. In addition, since the impedance matching is achieved by adjusting the gap from the resonator, it is inconvenient in real application, and an additional mounting area is required as much as the gap. Moreover, it is difficult to manufacture a resonator in an embedded PCB type or a film type which can maintain a miniaturization.